During abdominal ultrasound, the operator increases the frequency of the transducer from 3.5 MHz to 7 MHz to improve image resolution. What is the inevitable trade-off of using higher frequency ultrasound?

• A Increased Doppler shift artefact leading to colour blooming
• B Greater risk of bioeffects from increased thermal index
• C Reduced frame rate due to longer pulse repetition period
• D Decreased tissue penetration due to greater acoustic attenuation at higher frequencies ✓

Explanation

In diagnostic ultrasound, axial and lateral resolution improve with increasing frequency because the wavelength shortens (resolution is approximately 1-2 wavelengths). However, acoustic attenuation in tissue increases approximately linearly with frequency (approximately 0.5 dB/cm/MHz in soft tissue), meaning that higher frequency sound waves lose energy more rapidly as they propagate through tissue. The practical consequence is that high-frequency transducers (7-15 MHz) provide excellent near-field detail but cannot penetrate deeply, limiting their use to superficial structures. Low-frequency transducers (2-5 MHz) are required for deep abdominal and pelvic organs despite poorer resolution. This frequency-resolution-penetration trade-off is a fundamental principle of clinical ultrasound.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.